Some Issues in Fitness for Service Assessment of Wall Thinned CANDU Feeder Pipes

2008 ◽  
Author(s):  
John C. Jin ◽  
Seyun Eom ◽  
Raoul Awad
Keyword(s):  
Detailed Analysis ◽  
Pipe Wall ◽  
Limit Load ◽  
Nuclear Industry ◽  
Membrane Stress ◽  
Minimum Thickness ◽  
Accelerated Corrosion ◽  
Class 1 ◽  
Definition Of ◽  
Flow Accelerated Corrosion

Canadian CANDU® feeder pipes experiencing pipe wall thinning due to flow accelerated corrosion (FAC) are accepted for continued service after an engineering evaluation. This evaluation is based on the assumption that FAC degradation is manageable through a comprehensive inspection program and conservative engineering evaluations. The practice of the Canadian nuclear industry is to: establish a minimum acceptable wall thickness, compare the measured thickness to predictions from the previous outage to confirm the conservatism of the predictions in a condition assessment, and predict the thickness at the next inspection and compare against the minimum acceptable value in an operational assessment. If the thickness measured during outage does not meet the pre-established thickness criteria, the feeder should be replaced, unless it is demonstrated to be fit for service through a detailed analysis. The detailed analysis usually involves more complex methodologies which are subjected to regulatory reviews. Several issues have been raised in the fitness-for-service assessments of feeder pipes relating to the definition of primary membrane stress, interpretation of minimum thickness requirements, plasticity analysis, limit load analysis and the applicability of procedures given in Code Case N-597 to Class 1 feeder pipes. This paper presents the Canadian regulatory expectations on these issues.

An Analytical Solution for Piping Non-Planar Flaws

2014 ◽  
Author(s):  
Phuong H. Hoang ◽  
Chee W. Mak
Keyword(s):  
Cross Section ◽  
Nuclear Power ◽  
Pipe Wall ◽  
Axial Loading ◽  
Limit Load ◽  
Element Analysis ◽  
Axial Section ◽  
Accelerated Corrosion ◽  
Pressure Limit ◽  
Flow Accelerated Corrosion

Recent studies on the effect of multi-axis loading on piping non-planar flaws indicate that the ASME Section XI, Appendix C pressure limit load approach for planar axial flaws can be used for evaluation of non-planar flaws provided that the effect of multi axial loading is to be considered. Finite element analysis results presented in this paper also indicate that bending limit load for planar circumferential flaws can be used for evaluation of non-planar flaws subjected multi axial loading. These studies used idealized uniformly thin rectangular flaws whose projected flaw geometry on pipe cross section and on pipe axial section are the same as the circumferential flaw geometry and the axial flaw geometry defined ASME B&PV, Section XI Appendix C. Sample problems with actual pipe wall thinning flaws due to flow accelerated corrosion and pitting in nuclear power plant are utilized for a comparison of the proposed methodology with various methodologies currently used by the industry for locally thinning pipe flaw evaluations.

Technical Basis for the Assessment of Small Bore High Energy Piping With Lower Than Code Specified Design Minimum Thickness

2015 ◽  
Author(s):  
Xinjian Duan
Keyword(s):  
High Energy ◽  
Life Extension ◽  
Future Research ◽  
Structural Factors ◽  
Minimum Thickness ◽  
Accelerated Corrosion ◽  
Research Activities ◽  
Class 1 ◽  
Technical Basis ◽  
Flow Accelerated Corrosion

Wall thinning by Flow Accelerated Corrosion (FAC), Erosion-Cavitation (E-C), and fretting has been observed in carbon steel piping. At some locations, the predicted end-of-life wall thickness could be below the design minimum thickness required by ASME B&PV Code Section III, which is an extremely conservative analysis method. To support the life extension without replacement or repair, it is essential to demonstrate the fitness for service of degraded piping components that satisfy the mandatory structural factors with uncertainties explicitly identified and addressed in an integrated manner. The present paper discusses the key technical basis for a sound assessment of small bore high energy Class 1 piping with lower than Code specified design minimum thickness, and proposes some future research activities to further enhance the technical basis.

Effects of Flow Accelerated Corrosion on Piping Steady-State Vibration Evaluations

2003 ◽  
Author(s):  
Brian J. Voll
Keyword(s):  
Steady State ◽  
Nuclear Power ◽  
Power Plants ◽  
Pipe Wall ◽  
Vibration Monitoring ◽  
Accelerated Corrosion ◽  
Monitoring Programs ◽  
Wall Thinning ◽  
Piping Systems ◽  
Flow Accelerated Corrosion

Piping steady-state vibration monitoring programs were implemented during preoperational testing and initial plant startup at most nuclear power plants. Evaluations of piping steady-state vibrations are also performed as piping and component failures attributable to excessive vibration are detected or other potential vibration problems are detected during plant operation. Additionally, as a result of increased flow rates in some piping systems due to extended power uprate (EPU) programs at several plants, new piping steady-state vibration monitoring programs are in various stages of implementation. As plants have aged, pipe wall thinning resulting from flow accelerated corrosion (FAC) has become a recognized industry problem and programs have been established to detect, evaluate and monitor pipe wall thinning. Typically, the piping vibration monitoring and FAC programs have existed separately without interaction. Thus, the potential impact of wall thinning due to FAC on piping vibration evaluations may not be recognized. The potential effects of wall thinning due to FAC on piping vibration evaluations are reviewed. Piping susceptible to FAC and piping susceptible to significant steady-state vibrations, based on industry experience, are identified and compared. Possible methods for establishing links between the FAC and vibration monitoring programs and for accounting for the effects of FAC on both historical and future piping vibration evaluations are discussed.

Case Studies of Pulsed Eddy Current to Measure Wall Loss in Feedwater Piping and Heater Shells

2008 ◽  
Author(s):  
Marvin J. Cohn ◽  
Jordan W. Norton
Keyword(s):  
Eddy Current ◽  
Power Plants ◽  
Cost Effective ◽  
Nuclear Industry ◽  
Accelerated Corrosion ◽  
Pulsed Eddy Current ◽  
Catastrophic Failures ◽  
Recent Developments ◽  
Wall Loss ◽  
Flow Accelerated Corrosion

There have been several feedwater piping and heater shell failures in power plants caused by flow-accelerated corrosion (FAC). This failure mechanism may be one of the most important types of damage to find proactively because FAC damage has occasionally resulted in catastrophic failures and human fatalities. Predicting, detecting, and resolving significant FAC damage can significantly reduce future forced outages and increase personnel safety. This paper describes the implementation of recent developments to perform cost-effective FAC examinations. These advances include the use of specialized pulsed eddy current (PEC) hardware and software to scan for wall thinning without removing insulation. Recent results are based on the current version, MK II, of this equipment. The authors have performed more than 200 power plant projects with this PEC equipment, examining numerous pipes and shells. This work consists of more than 70 projects of wall loss examinations for the nuclear industry, including examinations of feedwater heater shells inside the condenser. Results of wall loss measurements regarding PEC average wall thickness (AWT) measurements, ultrasonic thickness examinations (UTTH), and the PEC evaluated Defect Algorithm are compared in this study.

C219 Velocity field characteristics at pipe-wall thinning position induced by Flow-Accelerated Corrosion

2010 ◽  
Vol 2010.15 (0) ◽  
pp. 367-368
Author(s):  
Masashi Tatematsu ◽  
Sheng Feng ◽  
Shingo Furuya ◽  
Masaya Kondou ◽  
Yoshiyuki Tsuji
Keyword(s):  
Velocity Field ◽  
Pipe Wall ◽  
Accelerated Corrosion ◽  
Wall Thinning ◽  
Flow Accelerated Corrosion

scholarly journals Flow-Accelerated Corrosion in Pipe Wall Downstream of Orifice for Water and Air-Water Bubble Flows

2016 ◽  
Vol 04 (03) ◽  
pp. 93-103 ◽  
Author(s):  
Toshihiko Shakouchi ◽  
Koichi Kinoshita ◽  
Koichi Tsujimoto ◽  
Toshitake Ando
Keyword(s):  
Pipe Wall ◽  
Accelerated Corrosion ◽  
Flow Accelerated Corrosion

Effects of Local Wall Thinning With Crack on Stress Intensity Factor for Pipes Subject to Combined Pressure and Bending

2019 ◽  
Author(s):  
Joy (Xiaoya) Tao ◽  
Lei Zhu
Keyword(s):  
Stress Intensity Factor ◽  
Finite Element ◽  
Stress Intensity ◽  
Intensity Factor ◽  
Nuclear Power ◽  
Power Plants ◽  
Limit Load ◽  
Minimum Thickness ◽  
Element Analysis ◽  
Accelerated Corrosion

Abstract At ageing power plants, local thinning of pipework or vessel is unavoidable due to erosion/corrosion or other reasons such as flow accelerated corrosion (FAC) — one of the common degradation mechanisms in pipework of nuclear power plant. Local thinning reduces the structure strength, resulting in crack initiation from the corrosion pit or welding defect when subject to cyclic loading. General practice is to use the minimum thickness of the thinned area to calculate both limit load and stress intensity factor (SIF) in performing Engineering Critical Assessment (ECA) using Failure Assessment Diagram (FAD). Using the minimum thickness is normally overly conservative as it assumes that thinning occurs grossly instead of locally, leading to unnecessary early repair/replacement and cost. Performing cracked body finite element analysis (FEA) can provide accurate values of limit load and SIF, but it is time consuming and impractical for daily maintenance and emergent support. To minimise the conservatisms and provide a guidance for the assessment of locally thinned pipework or vessel using existing handbook solutions, a study was carried out by the authors on the effect of local thinning on limit loads. The study demonstrates that local thinning has significant effect on limit load if the thinning ratio of thinning depth to original thickness is larger than 25%. It concluded that the limit load solutions given in handbooks (such as R6 or the net section method) are overly conservative if using the minimum local thickness and non-conservative if using the nominal thickness. This paper discusses the effect of local thinning on SIFs of internal/external defects using cracked body finite element method (FEM). The results are compared with R6 weight function SIF solutions for a cylinder. A modified R6 SIF solution is proposed to count for the effect of local thinning profile. Along with the previous published paper on limit load it provides comprehensive understanding and guidance for fracture assessment of the local thinned pipework and vessel.

Proposal of the Estimation Equation of Flow Accelerated Corrosion Under Water-Steam Two-Phase Flow

2013 ◽  
Author(s):  
Masaaki Satake ◽  
Kimitoshi Yoneda ◽  
Ryo Morita ◽  
Fumio Inada
Keyword(s):  
Flow Condition ◽  
Two Phase Flow ◽  
Pipe Wall ◽  
Prediction Equation ◽  
Phase Flow ◽  
Two Phase ◽  
Accelerated Corrosion ◽  
Water Steam ◽  
Flow Accelerated Corrosion ◽  
Thinning Rate

Flow accelerated corrosion (FAC) is one of the pipe wall thinning phenomena. There are a few prediction equations for FAC under the two-phase flow condition, but their accuracy is uncertain. In this study, these equations are summarized. A new prediction equation is proposed, in which the liquid film velocity near the wall is taken into account. Also, FAC experiments with water-steam two-phase flow are performed. The thinning rate is predicted by calculation and compared with the experimental value.

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